Material composite in strip form and its use, composite sliding element

ABSTRACT

The invention relates to a material composite in strip form, in which a layer consisting of a copper multicomponent alloy is permanently joined to a steel supporting layer, where the copper multicomponent alloy is composed of. [in % by weight]:
     Ni 1.0 to 15.0%,   Sn 2.0 to 12.0%,   remainder Cu and inevitable impurities,   optionally up to 5% manganese,   optionally up to 3% silicon,   optionally individually or in combination up to 1.5% Ti, Co, Cr, Al, Fe, Zn, Sb,   optionally individually or in combination up to 0.5% B, Zr, P, S,   optionally up to 25% Pb.   

     The invention also relates to a process for producing the material composite in strip form, to the use of the material composite and to a composite sliding element.

The invention relates to a material composite in strip form and its useand to a composite sliding element consisting of a material composite instrip form.

Copper alloys have been successfully used for bearing applications overthe course of decades. They satisfy the demands imposed particularlywell on account of their microstructure and properties. However, it hasbeen found that limits are imposed on conventional bronzes and complexbrass alloys under high thermal stresses.

As an alternative to conventional liners made from solid bearingmaterial, it is also known to use steel composite liners. To producethese, by way of example, strips of lead-containing tin bronzes areplated onto steels by rolling processes. However, bearing materials ofthis type comprising tin bronzes with tin contents of 4-8% by weight donot satisfy all the high demands imposed on the bearing materials in thehigh-stress environs of an engine compartment.

Document DE 199 63 385 C1 has disclosed a layer composite material forsliding bearings which has a higher specific load-bearing capacity andreduced wear rate. The layer composite material includes a carrierlayer, a bearing metal layer, a first interlayer of nickel, a secondinterlayer of nickel and tin as well as a sliding layer consisting ofcopper and tin. The sliding layer includes a tin matrix in whichtin-copper particles are intercollated, consisting of 39 to 55% byweight copper, remainder tin.

At high temperatures, as are encountered by sliding bearings in internalcombustion engines, the tin migrates into the second interlayer locatedbelow, resulting in a concentration of the tin-copper particles.

Furthermore, document DE 33 04 740 C2 has disclosed multilayer slidingbearings which comprise a solid metallic supporting body, a softermetallic carrying layer, for example made from an aluminum bearingalloy, and a sliding layer of a tin-containing, lead-based bearing alloyapplied by electrodeposition. An inlay double layer which includes acopper alloy layer is arranged between the carrying layer and thesliding layer.

Document EP 0 921 211 has also disclosed a layer composite material forsliding bearings having a carrier layer, a bearing metal layer of acopper alloy with a copper content of from 60 to 95% by weight or analuminum alloy with an aluminum content of from 60 to 96% by weight, adiffusion barrier layer and a sliding layer of a lead-free copper-tinalloy applied by electrodeposition.

The invention is based on the object of developing a material compositein strip form and a composite sliding bearing in such a way that both ahigh wear resistance and a high hot strength are produced.

In terms of a material composite in strip form, the invention isrepresented by the features of claim 1. A use of the material compositein strip form is described in claim 5, and a composite sliding elementis described in claim 6. The further dependent claims relate toadvantageous refinements and developments of the invention.

The invention encompasses a material composite in strip form, in which alayer consisting of a copper multicomponent alloy is permanently joinedto a steel supporting layer, where the copper multicomponent alloy iscomposed of [in % by weight]:

Ni 1.0 to 15.0%, Sn 2.0 to 12.0%,

remainder Cu and inevitable impurities,optionally up to 5% manganese,optionally up to 3% silicon,optionally individually or in combination up to 1.5% Ti, Co, Cr, Al, Fe,Zn, Sb,optionally individually or in combination up to 0.5% B, Zr, P, S,optionally up to 25% Pb.

The invention is based on the consideration that a high-performancematerial composite is provided, consisting of steel and a Cu—Ni—Sn alloypermanently joined to the steel. The purpose of the material compositeis to simultaneously offer very good wear resistance and, on account ofits use as a sliding element in an environment imposing high thermalstresses, an excellent hot strength.

The wrought Cu—Ni—Sn alloys according to the invention are spinodallysegregating systems, which are already known in principle as a solidmaterial used as bearing materials in engine manufacture. Thesematerials have good frictional and wear properties and a good resistanceto corrosion. The thermal stability is likewise excellent.

With these materials, having Ni contents of 1-15% and Sn contents of2-12%, it is possible to achieve degrees of cold-forming of up to 60%.In combination with soft-annealing, it is possible to produce thinstrips suitable for material composites. These strips can optionally beage-hardened in the temperature range between 300 and 500° C. As aresult, the material is work-hardened on account of the spinodalsegregation which takes place. Moreover, it is possible to formcontinuous or discontinuous precipitation.

This form of precipitation hardening is significantly superior to binarycopper-based alloys. To optimize the bonding strength between theCu—Ni—Sn alloy and the steel strip, the surfaces of both materials arepretreated. Thermal stability and strength combined, at the same time,with the required ductility is realized by the precipitation-hardenedmaterials according to the invention for bearing elements which areexposed to high demands.

The advantages achieved by the invention compared to solid liners are inparticular that with the material composite the demands relating to themechanical properties and the tribological properties can be optimizedseparately from one another by the combination of steel and a coppermulticomponent alloy layer. The materials properties of both partners inthe composite can be optimally adapted to the particular requirements bymeans of rolling, age-hardening and homogenization annealing. By way ofexample, it is also possible for a softer or harder coppermulticomponent alloy layer to be combined with the steel supportinglayer by means of mechanical and thermal treatments. The combination ofthe two materials in one material composite produces materialsproperties which are eminently suitable for sliding elementapplications.

In this context, an inexpensive structure results from the fact that thevolumetric content and the weight content of the steel carrier materialare greater than the content of the functional material comprising thecopper multicomponent alloys.

In a particularly preferred embodiment of the invention, the coppermulticomponent alloy may be composed of [in % by weight]:

Ni 1.0 to 15.0%, Sn 2.0 to 12.0%, Mn 0.1 to 2.5%, Si 0.1 to 1.5%,

remainder Cu and inevitable impurities,optionally individually or in combination up to 1.5% Ti, Co, Cr, Al, Fe,Zn, Sb,optionally individually or in combination up to 0.5% B, Zr, P, S.

This pursues the objective of further improving the wear resistance ofCu—Ni—Sn alloys by forming hard intermetallic phases. These furtherhard-material phases are manganese-nickel silicides. Cu—Ni—Sn alloysalready have very good properties in terms of the sliding properties,resistance to corrosion and resistance to relaxation at roomtemperature. However, the hard phases which are formed reduce thesusceptibility to adhesion in the mixed friction range and also furtherincrease the hot strength and ductility at elevated temperatures.

Surprisingly, by combining the microstructural constituents whichcontribute to wear resistance with a spinodally segregating alloy of theCu—Ni—Sn system, it is possible on the one hand to reduce the run-inrequirements resulting from wear at the start of the application ofstresses and on the other hand a Cu—Ni—Sn—Mn—Si material of this typealso proves to have a good hot strength and a sufficient ductility.

The supporting layer may advantageously consist of deep-drawing steel,quenched and tempered steel or case-hardening steel. Furtherhigh-strength steels may also be considered.

The layer consisting of the copper multicomponent alloy mayadvantageously have a thickness of from 0.1 to 3 mm. Strips of thecopper multicomponent alloy can be rolled down to this thickness bymeans of a suitable thermomechanical treatment.

In terms of the process, the layer consisting of the coppermulticomponent alloy can be rolled or cast or sintered onto the steelsupporting layer. For this purpose, in the case of rolling, the surfaceof the strip material of the supporting layer and that of the coppermulticomponent alloy can be pretreated and cleaned. In the simplestpossible case, this is done by a mechanical pretreatment using brushes.

The roll-clad strips may advantageously be particularly suitable for theproduction of composite sliding elements, for example in the form ofrolled liners and thrust washers. This alloy can also be used for plugconnectors used in electrical engineering.

In a preferred configuration of the invention, a composite slidingelement may consist of the material composite in strip form according tothe invention, which before and/or after shaping has undergone at leastone heat treatment at 300 to 500° C., causing the material to bework-hardened as a result of the spinodal segregation which takes place.

A composite sliding element made from the material composite in stripform according to the invention, before and/or after shaping, hasadvantageously undergone at least one heat treatment at 600 to 800° C.The heat treatment in this range leads to homogenization, whereby thematerial becomes softer.

Alternatively, a composite sliding element may undergo a combination ofat least one solution anneal at 600 to 800° C. and at least oneage-hardening treatment at 300 to 500° C. The materials properties ofthe copper multicomponent alloy can be optimally matched to its partnerin the composite, namely steel, by means of a homogenization anneal andthe hardening of the material during age-hardening or rolling.

In a preferred configuration of the invention, an interlayer may bearranged between the surface of the steel supporting layer and the layerconsisting of the copper multicomponent alloy.

This interlayer is intended in particular to prevent diffusion phenomenaat the interface between the copper multicomponent alloy and the steeland if appropriate also to boost the bonding ability of both partners.

In a further preferred configuration, lubricating pockets may bearranged in the layer consisting of the copper multicomponent alloy.

Exemplary embodiments of the invention are explained in more detail onthe basis of the following examples and the optical microscopy image,shown in FIG. 1 of a material composite comprising a CuNiSn alloy and asteel strip.

EXAMPLE 1

For the tests, the applied material was CuNi6Sn6 in the as-rolled andsoft-annealed state, and the base material used was steel in variousstates. The specimens were treated with brushes and then cleaned.

This was immediately followed by rolling with different reductions perpass. The starting thickness of the strips of the copper multicomponentalloy was approx. 3 mm. The different strip thicknesses of the basematerial were 1.5, 3 and 5 mm. The width of the copper multicomponentalloy was approx. 0.1-0.3 mm less than that of the base material.Rolling forces, moments and outlet temperatures were measured. In eachcase five variations per combination were carried out for each materialstate having the above-mentioned thicknesses of the base material. Therolling tests showed that CuNi6Sn6 can be readily plated onto steel withgood material bonding.

FIG. 1 shows an optical microscopy image of a cross section through amaterial composite made up of a CuNiSn alloy 1 and a steel strip 2. Thecomposite bearing material can be used by roll-cladding in the as-rolledstate, in the soft-annealed state and in the age-hardened state. Thehomogenization temperatures are between 500 and 800° C., anage-hardening takes place at temperatures between 300 and 500° C.

EXAMPLE 2

The following text describes a process for producing a materialcomposite comprising the copper multicomponent alloy for slidingelements, such as thrust washers and bearing liners. In this process, alead-free bearing material from the Cu—Ni—Sn system is applied todeep-drawing steel by melting and casting. The lead-free bearingmaterial was cast on at a temperature of 1000 to 1200° C., with thelayer microstructure being formed from α-phase with continuous anddiscontinuous precipitations. The material composite comprising steeland the Cu—Ni—Sn alloy was annealed at temperatures between 600 and 800°C., and then the surface of the layer was removed by milling. Theselayer bearing materials can be used both in the as-cast state and in theage-hardened state for sliding bearing elements. The age-hardening wascarried out at temperatures between 300 and 500° C.

The cast microstructure of the bearing layer was wrought bythermomechanical treatments, such as rolling and annealing. The stripscan be cold-rolled with degrees of deformation of between 10 and 60% andthen annealed at temperatures between 500 and 800° C. It has been foundthat the composite bearing material can be used in all its variousstates, i.e. in the as-cast state, in the wrought state and in theage-hardened state, for sliding elements.

EXAMPLE 3

In further series of tests, ingots with different Mn—Si ratios were castand then cold-worked further. The alloy variants tested are summarizedin Table 1. The cast ingots were homogenized in the temperature rangebetween 700 and 800° C. and then milled. Strips with thicknesses ofbetween 2.5 and 2.85 mm were then produced by a plurality ofcold-forming stages and intermediate annealing steps. The strips werecold-rolled and then annealed in the temperature range between 700 and800° C. in order to achieve sufficient cold-formability.

TABLE 1 Cu Ni Sn Mn Si Cu − Ni − [% by [% by [% by [% by [% by Sn + Mn +Si weight) weight] weight] weight] weight] Variant 1 Remainder 5.6–6.05.2–5.6 1.7–2.0 0.2–0.3 Variant 2 Remainder 5.6–6.0 5.2–5.6 1.3–1.60.2–0.3 Variant 3 Remainder 5.6–6.0 5.2–5.6 1.3–1.6 0.5–0.7 Variant 4Remainder 5.6–6.0 5.2–5.6 0.8–1.0 0.1–0.3 Variant 5 Remainder 5.6–6.05.2–5.6 0.8–1.0 0.3–0.5 Variant 6 Remainder 5.6–6.0 5.2–5.6 0.4–0.60.4–0.6 Variant 7 Remainder 5.6–6.0 5.2–5.6 0.9–1.1 0.9–1.1 Variant 8Remainder 5.6–6.0 5.2–5.6 1.8–2.1 0.5–0.6 Variant 9 Remainder 5.6–6.05.2–5.6 1.8–2.1 0.9–1.1

As expected, it was confirmed that the cold-formability of the Cu—Ni—Snalloy modified with silicides is slightly lower than that of a Cu—Ni—Snalloy without further silicide phases.

In a further process step, strips of this type are combined to form astrong material composite by roll-cladding processes. The tribologicaltests demonstrated that the silicide-modified Cu—Ni—Sn alloys had asignificantly lower coefficient of friction than the unmodified variant.This new modified alloy is therefore suitable in particular as a primarymaterial for use as a sliding element (liners, thrust washers, etc.) inthe automotive industry for engines, transmissions and hydraulics.

However, over and beyond the values indicated in the table, it has beenfound that modified Cu—Ni—Sn variants with an Si content of up to 1.5%by weight and a Mn content of up to 2.5% by weight can be manufacturedwith improved materials properties. Further laboratory tests todemonstrate this have likewise already been carried out, confirming thelimit values.

In particular, it has been ensured that with an Si content of up to 0.7%by weight and an Mn content of up to 1.6% by weight manufacturing isactually possible without problems from a manufacturing technologyperspective. If higher silicon and manganese contents are used,corresponding adjustments in line with standard measures should beperformed with regard to the casting parameters.

However, difficulties, in particular caused by cracks at the edges ofthe strip material, are likely during further processing if the siliconand/or manganese contents exceed the indicated maxima of 3% by weightand 5% by weight, respectively.

The CuNiSn alloy contains finely distributed manganese-nickel silicideswhich are embedded in the alloy matrix. These silicides, as the firstprecipitation in the melt, are formed as early as the temperature rangearound 1100° C. If the melt composition is selected appropriately, theavailable silicon and manganese are precipitated with a nickel contentwhich is present in excess to form the silicide. The nickel contentconsumed in the silicide can be correspondingly taken into account forthe subsequent formation of the matrix by using a higher nickel contentin the melt.

The composition of the silicides does not necessarily have to correspondto a predetermined stoichiometry. Depending on the procedure adopted,determined in particular by the cooling rate, ternary intermetallicphases precipitate in the form of the silicides of type (Mn,Ni)_(x)Si,which are in the range between the binary boundary phases Mn₅Si₃ andNi₂Si.

1. Material composite in strip form, in which a layer consisting of acopper multicomponent alloy is permanently joined to a steel supportinglayer, where the copper multicomponent alloy is composed of [in % byweight]: Ni 1.0 to 15.0%, Sn 2.0 to 12.0%, remainder Cu and inevitableimpurities, optionally up to 5% manganese, optionally up to 3% silicon,optionally individually or in combination up to 1.5% Ti, Co, Cr, Al, Fe,Zn, Sb, optionally individually or in combination up to 0.5% B, Zr, P,S, optionally up to 25% Pb.
 2. Material composite in strip formaccording to claim 1, characterized in that the copper multicomponentalloy is composed of [in % by weight]: Ni 1.0 to 15.0%, Sn 2.0 to 12.0%,Mn 0.1 to 2.5%, Si 0.1 to 1.5%, remainder Cu and inevitable impurities,optionally individually or in combination up to 1.5% Ti, Co, Cr, Al, Fe,Zn, Sb, optionally individually or in combination up to 0.5% B, Zr, P,S.
 3. Material composite in strip form according to claim 1,characterized in that the supporting layer consists of deep-drawingsteel, quenched and tempered steel or case-hardening steel.
 4. Materialcomposite in strip form according to claim 1, characterized in that thelayer consisting of the copper multicomponent alloy has a thickness offrom 0.1 to 3 mm.
 5. Use of the material composite in strip formaccording to claim 1 for composite sliding elements or plug connectors.6. Composite sliding element consisting of a material composite in stripform according to claim 1, characterized in that before and/or aftershaping it has undergone at least one heat treatment at 300 to 500° C.7. Composite sliding element consisting of a material composite in stripform according to claim 1, characterized in that before and/or aftershaping it has undergone at least one heat treatment at 600 to 800° C.8. Composite sliding element consisting of a material composite in stripform according to claim 1, characterized in that it has undergone acombination of at least one solution anneal at 600 to 800° C. and atleast one age-hardening treatment at 300 to 500° C.
 9. Composite slidingelement according to claim 6, characterized in that an interlayer isarranged between the surface of the steel supporting layer and the layerconsisting of the copper multicomponent alloy.
 10. Composite slidingelement according to claim 6, characterized in that lubricating pocketsare arranged in the layer consisting of the copper multicomponent alloy.